Retaking control of self-driving cars risky: study

Retaking back control of an autonomous car affects human steering behaviour, according to a new Stanford study that may help in the design of future self-driving vehicles.
When human drivers retake control of an autonomous car, the transition could be problematic, depending on how conditions have changed since they were last at the wheel, researchers said.
"There is this physical change and we need to acknowledge that people's performance might not be at its peak if they have not actively been participating in the driving," said Holly Russell, former graduate student at Stanford University in the US.
The trouble the drivers had getting used to different driving conditions was not enough to cause them to miss their turns, however it was noticeable in the researcher's measurements and by watching them wobble the wheel to account for over and understeering.

These challenges bring up the possibility that, depending on the particulars of the driver, the driving conditions and the autonomous system being used, the transition back to driver-controlled driving could be an especially risky window of time, researchers said.
Twenty two study participants drove a 15-second course consisting of a straightaway and a lane change. Then they took their hands off the wheel and the car took over, bringing them back to the start.

After going through this process four times, they drove the course 10 additional times with steering conditions that were modified to represent changes in speed or steering that may occur while the car drives itself.

Changing the steering ratio from the standard 15:1 to 2:1 simulated the more sensitive steering feel drivers experience at a higher speed.
This modification made the car turn more sharply to simulate the way less steering wheel movement is needed to make a lane change at a high speed versus at a low speed.
All drivers were given advance warning of the changes and had some opportunity to probe the difference during the straightaway.
Regardless, during the altered steering ratio trials, the drivers' steering manoeuvres differed significantly from their paths previous to the experimental modifications.
"Even knowing about the change, being able to make a plan and do some explicit motor planning for how to compensate, you still saw a very different steering behaviour and compromised performance," said Lene Harbott, research associate in the Revs Programme at Stanford.

The participants also drove the course another six times, after being taken back to the start by the car, with the original conditions restored.
Again, drivers who experienced the steering ratio change displayed a clear period of adjustment, undershooting the steering wheel turning required to complete their lane change.
The research was published in the journal Science Robotics.